Transportation vehicles, such as automobiles, watercraft and in particular aircrafts frequently contain low weight materials to reduce fuel consumption. To achieve this purpose sandwich composites with honeycomb cores are frequently employed instead of solid structures. Also in the construction of buildings such honeycomb structures have found wide application. Typically, the honeycomb core is formed by a metal, e.g. aluminium, or fibreglass or composites, and the cells between the honeycomb core are void. The size of the void cells in a honeycomb structure influences the mechanical properties of the structure. The bigger the size the greater the weight reduction but the greater may be the loss of mechanical strength. Void cells in honeycomb structures may typically range from 5 mm up to 10 cm in at least one or all three dimensions. To counteract the potential loss of mechanical strength compared to solid structures, the cells of the honeycomb structure are partially or completely filled with filler materials (core fillers). Epoxy resin based compositions may be used for this purpose, for example those described in international patent application WO2010/117669 A1. The external surfaces of the honeycomb structures are often covered by facesheets, i.e. layers of resins, for example epoxy resins or phenolic resins, to further improve the overall stability of the honeycomb structures. Honeycomb structures covered by facesheets are also termed sandwhich composites with a honeycomb core. Composite materials, in particular prepregs (preimpregnated fibers) are increasingly used as face sheets because of their good fire retardant properties which are particularly important to the aircraft industry. It is often necessary to drill holes or mill patterns in the honeycombs, for example, during assembly or when installing the honeycombs at the desired place of a vehicle or building. This can lead to delamination of the facesheets from the epoxy-based core filler and requires subsequent application of adhesives. Also milling and cutting of the facesheets may lead to rough edges of the holes and structures formed, often requiring subsequent sanding to smoothen the rough edges in particular when cutting or milling through the interface of facesheet and core filler. This problem occurs with facesheets based on composites, in particular composites. Therefore, there is a need to provide improved core filler compositions for honeycomb structures.